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BACKGROUND CONTEXT Dysphagia following anterior cervical discectomy and fusion (ACDF) is a common complication, the etiology of which has not been established. Given that one potential mechanism for dysphagia is local tissue edema, it is thought that a greater number of operative levels may result in higher dysphagia rates. However, prior reports comparing one-level to two-level ACDF have shown varying results. PURPOSE To determine if there is a difference in dysphagia between one-level and two-level ACDF. STUDY DESIGN/SETTING Retrospective review of prospectively collected data. PATIENT SAMPLE Patients who underwent one- or two-level ACDF with a plate-graft construct by a single-surgeon at a high-volume academic medical center. OUTCOME MEASURES Neck Disability Index, Visual Analog Scale for neck pain and arm pain, Short Form-12 physical and mental health components, and Swallowing Quality of Life (SWAL-QOL) Questionnaire. METHODS Patient demographics, operative data, and patient-reported outcome measures (PROMs; Neck Disability Index, Visual Analog Scale, Short Form-12, and SWAL-QOL) of patients undergoing one- and two-level ACDF were compared using Fisher exact test for categorical variables and Student's t test for continuous variables. Regression analyses were conducted to identify factors associated with 6- and 12-week SWAL-QOL scores in order to determine whether the number of surgical levels impacts these outcomes. RESULTS Fifty-eight patients (22 one-level and 36 two-level ACDF) were included. Patients undergoing two-level fusions were older (54.17+8.67 vs 48.06+10.68 years, p=.02) and had longer operative times (69.08+10.51 vs 53.5+14.35 minutes, p 61.5 minutes had a sensitivity and specificity of 62.1% for worse dysphagia scores at 6 weeks compared with baseline. CONCLUSIONS The results of our study indicate that there is no difference in the degree of postoperative dysphagia in one- versus two-level ACDF. However, other variables associated with increased postoperative dysphagia in our population included younger age, male sex, procedural time >61.5 minutes, and worse preoperative dysphagia. Larger studies are required to confirm these findings and identify additional risk factors for postoperative dysphagia.

We prove a strictification theorem for cartesian closed bicategories. First, we adapt Power’s proof of coherence for bicategories with finite bilimits to show that every bicategory with bicategorical cartesian closed structure is biequivalent to a 2-category with 2-categorical cartesian closed structure. Then we show how to extend this result to a Mac Lane-style “all pasting diagrams commute” coherence theorem: precisely, we show that in the free cartesian closed bicategory on a graph, there is at most one 2-cell between any parallel pair of 1-cells. The argument we employ is reminiscent of that used by Čubrić, Dybjer, and Scott to show normalisation for the simply-typed lambda calculus (Čubrić et al., 1998). The main results first appeared in a conference paper (Fiore and Saville, 2020) but for reasons of space many details are omitted there; here we provide the full development.

Study design Prospective cohort study. Objective To examine preoperative urinary cross-linked n-telopeptide (uNTx) and assess for association with fusion rates in patients undergoing single and multi-level anterior cervical decompression and fusion (ACDF). Summary of background data Although high rates of fusion have been reported for ACDF, the risk of pseudarthrosis remains substantial. An established marker of bone turnover, uNTx may prove useful as a predictor of fusion. Methods Patients undergoing primary ACDF with allograft/plating technique from 2015 to 2017 by a single surgeon were consecutively enrolled and preoperative uNTx was collected. Patients undergoing revision, with creatinine >1.2, and with improperly-collected uNTx were excluded. Demographics, laboratory values, and fusion status were assessed at 6 months, 1 year, and 2 years postoperatively. Results Of the 97 patients enrolled, 69 met inclusion criteria. Of included cases, 41%, 33%, 18%, and 8% underwent 1-, 2-, 3-, and 4-level ACDF, respectively. Overall, fusion rates were 37.3%, 70.9%, and 95.3% at 6 months, 1 year, and 2 years, respectively. uNTx was higher in the fusion group (31.1 vs. 22.2, P = 0.001) at 6 months and 1 year (30.0 vs. 21.0, P = 0.006), with no difference at 2 years. No differences were identified in the proportion of smokers, immunomodulatory agents, corpectomies, or fusion levels between groups. Multivariate regression analysis demonstrated that uNTx is an independent predictor of fusion (odds ratio, OR, 1.124, P = 0.003). Both groups experienced improvements in NDI and VAS neck pain at 6 months with no significant differences noted between groups. Of 16 patients with pseudarthrosis at 1 year, 2 underwent posterior cervical fusion for symptoms. Conclusion Preoperative uNTx was greater in patients with successful ACDF fusion compared with patients with pseudarthrosis at 6 months and 1 year. A negative correlation was found between preoperative uNTx and motion on dynamic imaging. These results suggest that uNTx could serve to identify patients at risk for pseudarthrosis after ACDF. Level of evidence 3.

The glueing construction, defined as a certain comma category, is an important tool for reasoning about type theories, logics, and programming languages. Here we extend the construction to accommodate ‘2-dimensional theories’ of types, terms between types, and rewrites between terms. Taking bicategories as the semantic framework for such systems, we define the glueing bicategory and establish a bicategorical version of the well-known construction of cartesian closed structure on a glueing category. As an application, we show that free finite-product bicategories are fully complete relative to free cartesian closed bicategories, thereby establishing that the higher-order equational theory of rewriting in the simply-typed lambda calculus is a conservative extension of the algebraic equational theory of rewriting in the fragment with finite products only.

Purpose Cervical spines previously posteriorly instrumented and fused with a kyphotic deformity represent a surgical challenge. Current treatment strategies include C7 pedicle subtraction osteotomy or a posterior-anterior-posterior approach, which carry the risk of significant complications. The objective of this study was to attempt to achieve lordosis with multiple anterior cervical discectomy and fusion (ACDF) cages to overpower the posterior instrumentation. Methods Four adult cadaveric specimens were selected and underwent C3–C7 posterior laminectomy with posterior instrumentation in a kyphotic alignment using a 3.5-mm titanium screw-rod system. Next, ACDF from C3 to C7 was performed with 15° lordotic cages to restore cervical lordosis. Posterior instrumentation was then inspected for failure. Fluoroscopic images were obtained to calculate total construct lordosis and change in segmental lordosis. CT scans were obtained after ACDF to assess for loosening, instrumentation failure, endplate damage, or impaction. Bone mineral density was calculated on CT scans. Results Age ranged from 59 to 82, and all specimens were male. No gross instrumentation failure was observed. Mean pre-ACDF lordosis between C3 and C7 was 0° (–5° to 5°). Post-ACDF lordosis increased to 37° (35°–38°). Mean segmental lordosis achieved with no endplate destruction was 13.1° (8°–17°). T scores for the cadavers were –0.5, –0.5, –3.2, and –5.1. Two levels of impaction were observed (12.5%). Failure of bone screw interface occurred in the cadaver, with a T score of –5.1 in the middle of the construct. Conclusion Our study demonstrates the validity of overpowering posterior instrumentation through multiple level ACDF with lordotic cages. This may obviate the need to perform posterior-anterior-posterior procedures. Level of Evidence Level III

OBJECTIVEThe authors’ aim in this study was to evaluate whether sagittal plane correction can be obtained from the front by overpowering previous posterior instrumentation and/or fusion with hyperlordotic anterior lumbar interbody fusion (ALIF) cages in patients undergoing revision surgery for degenerative spinal conditions and/or spinal deformities.METHODSThe authors report their experience with the application of hyperlordotic cages at 36 lumbar levels for ALIFs in a series of 20 patients who underwent revision spinal surgery at a single institution. Included patients underwent staged front-back procedures: ALIFs with hyperlordotic cages (12°, 20°, and 30°) followed by removal of posterior instrumentation and reinstrumentation from the back. Patients were divided into the following 2 groups depending on the extent of posterior instrumentation and fusion during the second stage: long constructs (≥ 6 levels with extension into thoracic spine and/or pelvis) and short constructs (< 6 levels). Preoperative and postoperative standing radiographs were evaluated to measure segmental lordosis (SL) along with standard sagittal parameters. Radiographic signs of pseudarthrosis at previously fused levels were also sought in all patients.RESULTSThe average patient age was 54 years (range 30–66 years). The mean follow-up was 11.5 months (range 5–26 months). The mean SL achieved with 12°, 20°, and 30° cages was 13.1°, 19°, and 22.4°, respectively. The increase in postoperative SL at the respective surgically treated levels for 12°, 20°, and 30° cages that were used to overpower posterior instrumentation/fusion averaged 6.1° (p < 0.05), 12.5° (p < 0.05), and 17.7° (p < 0.05), respectively. No statistically significant difference was found in SL correction at levels in patients who had pseudarthrosis (n = 18) versus those who did not (n = 18). The mean overall lumbar lordosis increased from 44.3° to 59.8° (p < 0.05). In the long-construct group, the mean improvement in sagittal vertical axis was 85.5 mm (range 19–249.3 mm, p < 0.05). Endplate impaction/collapse was noted in 3 of 36 levels (8.3%). The anterior complication rate was 13.3%. No neurological complications or vascular injuries were observed.CONCLUSIONSALIF in which hyperlordotic cages are used to overpower posterior spinal instrumentation and fusion can be expected to produce an increase in SL of a magnitude that is roughly half of the in-built cage lordotic angle. This technique may be particularly suited for lordosis correction from the front at lumbar levels that have pseudarthrosis from the previous posterior spinal fusion. Meticulous selection of levels for ALIF is crucial for safely and effectively performing this technique.

Retrospective review of prospectively collected data.To investigate if zero profile devices offer an advantage over traditional plate/cage constructs for dysphagia rates in single level anterior cervical discectomy and fusion (ACDF).Dysphagia rates following ACDF have been reported to be as high as 83%, most cases are self-limiting, but chronic dysphagia can continue in up to 35% of patients. Zero profile devices were developed to limit dysphagia, and other plate specific complications, however the literature is currently divided regarding their efficacy.Dysphagia was assessed by swallowing quality of life (SWAL-QOL) scores preoperatively, at 6 weeks and 12 weeks. Patient reported outcome measures (PROMs) including visual analog scale (VAS) and Neck Disability Index (NDI) were collected preoperatively, at 6 weeks and at 6 months. Univariate and multivariate regression analysis was conducted with SWAL-QOL score as the dependent variable.Sixty-four patients were included, 41 received a zero profile device, and 23 received plate-graft construct. Both groups were similar regarding patient demographics, except operative time, with the zero-profile group having a shorter procedure time than the cage-plate group (44.88 ± 6.54 vs. 54.43 ± 14.71 min, P = 0.001). At all timepoints dysphagia rates were similar between the groups. Regression analysis confirmed preoperative SWAL-QOL and operative time were the only significant variables. PROMs were also similar between groups at all time points, except VAS neck at 6 months, which was lower in the plate-graft group (1.05 ± 1.48 vs. 3.43 ± 3.21, P = 0.007).Operative time and preoperative SWAL-QOL scores are predictive of dysphagia in single level ACDF. Zero profile devices had a significantly shorter operative time, and may provide a benefit in dysphagia rates in this regard.3.

Sagittal alignment is an important consideration in spine surgery. The literature is conflicted regarding the effect of minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) on sagittal parameters and the role of expandable cage technology.To compare lordosis generated by static and expandable cages and to determine what factors affect postoperative sagittal parameters.Preoperative regional lordosis (RL), segmental lordosis (SL), and posterior disc height (PDH) were compared to postoperative values in single-level MI-TLIF performed using expandable or static cages. Patients were stratified based on preoperative SL: low lordosis (15 degrees), moderate lordosis (15-25 degrees), and high lordosis (25 degrees). Regression analyses were conducted to determine factors associated with postoperative SL and PDH.Of the 171 patients included, 111 were in the static and 60 in the expandable cohorts. Patients with low preoperative lordosis experienced an increase in SL and maintained RL regardless of cage type. Those with moderate to high preoperative lordosis experienced a decrease in SL and RL with the static cage, but maintained SL and RL with the expandable cage. Although both cohorts showed an increase in PDH, the increase in the expandable cohort was greater. Preoperative SL was predictive of postoperative SL; preoperative SL, preoperative PDH, and cage type were predictive of postoperative PDH.Expandable cages showed favorable results in restoring disc height and maintaining lordosis in the immediate postoperative period. Preoperative SL was the most significant predictor of postoperative SL. Thus, preoperative radiographic parameters and goals of surgery should be important considerations in surgical planning.

Intervertebral disc disease is a prevalent and costly clinical problem in the United States. Disease-modifying therapies applied at the early stages of disease are desirable compared to the traditional and variably effective surgical options for end-stage disease. A better understanding of the normal intervertebral disc and the molecular and cellular basis of disc degeneration has led researchers to investigate innovative therapies. Specifically the developments of biomaterial-based hydrogels and annular patches, cell implantation, growth factor modulation, and gene transduction techniques all hold clinical promise. The most powerful therapy may combine several of these modalities to achieve long-standing results.

BACKGROUND Transforaminal lumbar interbody fusion (TLIF) is a well-accepted surgical technique for the treatment of degenerative spinal conditions and spinal deformity. The TLIF procedure can be performed open or using minimally invasive techniques. While several studies have found that minimally invasive TLIF (MI-TLIF) has advantages over open TLIF procedures with less blood loss, postoperative pain and hospital length of stay, opponents of the minimally invasive technique cite the lack of restoration of lumbar lordosis as a major drawback. With the increasing awareness of restoring sagittal alignment parameters in degenerative and deformity procedures, surgeons should understand the capabilities of different procedures to achieve surgical goals. To our knowledge, few studies have specifically studied the radiographic restoration of lumbar lordosis after MI-TLIF procedures. The purpose of this study was to perform a systematic review of the literature describing the sagittal lumbar radiographic parameter changes after MI-TLIF. METHODS Following PRISMA guidelines, systematic review was performed. With the assistance of a medical librarian, a highly-sensitive search strategy formulated on 1/19/2018 utilized the following search terms: “minimally invasive procedures,” “transforaminal lumbar interbody fusion,” “lumbar interbody fusion,” “diagnostic imaging,” “radiographs,” “radiography,” “x-rays,” “lordosis,” “lumbar vertebrae,” “treatment,” “outcome,” and “lumbosacral” using Boolean operators ‘AND’ and ‘OR’. Three databases were searched (PubMed/Medline, Embase, and Cochrane Library). An online system ( www.covidence.org ) was used to standardize article review. All studies were independently analyzed by two investigators and discrepancies mitigated by a third reviewer. Study selection for each cycle was Yes/No/Maybe. Cycles were: (1) (Title/Abstract); (2) (Full Text); (3) (Extraction). Inclusion criteria were: (1) All study designs, (2) MI-TLIF procedures, (3) Reporting total lumbar lordosis (LL) and/or segmental lordosis (SL) pre- and postoperatively. Exclusion criteria were: (1) non MI-TLIF procedures (ALIF, XLIF, LLIF, conventional TLIF, OLIF), (2) No reported LL or SL. RESULTS The search yielded 4,036 results with 836 duplicates leaving 3,200 studies for review. Cycle 1 eliminated 3,153 studies as irrelevant, thus, 47 were eligible for full-text review. Cycle 2 excluded 31 studies for No English full text (9), Oral/Poster (8), Wrong intervention/outcome (10), Duplicate listing (2), Full text not available (1), Literature review (1) resulting in 16 included studies. Study designs were: Randomized-controlled trial (3), Case series (6) and Retrospective (7). Mean # of subjects were 32.0 (range 8–95). Weighted-mean LL was 39.6°±9.2 (range 28–57) and postoperative LL was 45.0°±7.4 (range 36–67) with a LL post-pre difference of 5.2°±5.9 (range −7 to 15). Weighted-mean preoperative SL was 12.7°±4.3 (range 5–21) and postoperative SL was 15.0°±4.5 (range 5–22) with a SL post-pre difference of 2.1°±1.7 (range 0–8). CONCLUSIONS The current literature on MI-TLIF and restoration of LL/SL is limited to 16 published studies, 44% of which are retrospective. The published evidence supporting LL and SL restoration with MI-TLIF is sparse with variable results. This systematic review demonstrates the need for future high-level studies to fully elucidate the capabilities of MI-TLIF procedures for restoring lumbar and segmental lordosis.

OBJECTIVE The aim of this study was to evaluate the segmental correction obtained from 20° and 30° hyperlordotic cages (HLCs) used for anterior lumbar interbody fusion in staged anterior and posterior fusion in adults with degenerative spinal pathology and/or spinal deformities. METHODS The authors report a retrospective case series of 69 HLCs in 41 patients with adult degenerative spine disease and/or deformities who underwent staged anterior, followed by posterior, instrumentation and fusion. There were 29 females and 12 males with a mean age of 55 years (range 23–76 years). The average follow-up was 10 months (range 2–28 months). Radiographic measurements of segmental lordosis and standard sagittal parameters were obtained on pre- and postoperative radiographs. Implant subsidence was measured at the final postoperative follow-up. RESULTS For 30° HLCs, the mean segmental lordosis achieved was 29° (range 26°–34°), but in the presence of spondylolisthesis this was reduced to 19° (range 12°–21°) (p < 0.01). For 20° HLCs, the mean segmental lordosis achieved was 19° (range 16°–22°). The overall mean lumbar lordosis increased from 39° to 59° (p < 0.01). The mean sagittal vertical axis (SVA) reduced from 113 mm (range 38–320 mm) to 43 mm (range −13 to 112 mm). Six cages (9%) displayed a loss of segmental lordosis during follow-up. The mean loss of segmental lordosis was 4.5° (range 3°–10°). A total complication rate of 20% with a 4.1% transient neurological complication rate was observed. The mean blood loss per patient was 240 ml (range 50–900 ml). CONCLUSIONS HLCs provide a reliable and stable degree of segmental lordosis correction. A 30° HLC will produce correction of a similar magnitude to a pedicle subtraction osteotomy, but with a lower complication rate and less blood loss.

Background: Surgical correction of valgus deformity of the hindfoot has traditionally been via a lateral incision, often complicated by wound healing problems and sural nerve damage. Potential advantages of a medial approach especially for a valgus deformity include excellent wound healing, no risk of damage to the sural nerve and extensibility of the approach to include additional procedures such as navicular fusion or tendon transfer if indicated. Materials and Methods: We present a retrospective review of 18 consecutive patients with valgus deformity of the hindfoot, all undergoing arthrodesis via a medial approach. Indications included osteoarthritis, tibialis posterior dysfucntion, post-traumatic arthritis and rheumatoid arthritis. Results: All wounds healed by primary intention and there were no postoperative neurovascular complications. The mean preoperative subtalar valgus deformity was 32 (range, 12 to 49) degrees, which was improved to mean postoperative valgus deformity of 17 (range, 10 to 25) degrees. Fusion following the primary surgery was achieved in all but one of the patients (a heavy smoker and post-traumatic arthritis), with the mean time to fusion being 5.6 months. Conclusion: We provide further evidence to support previous documentation in the literature that the medial approach for the correction of hindfoot valgus deformity can be successfully used to achieve excellent exposure of the subtalar joint in order to correct the valgus deformity, avoiding the risks of wound healing and nerve damage associated with a lateral approach. Level of Evidence: IV, Retrospective Case Series

BACKGROUND CONTEXT Sagittal alignment is becoming an increasingly important consideration in minimally invasive spine surgery. Single level minimally invasive transforaminal lumbar interbody fusion (MIS TLIF) can have immediate impact on segmental and regional sagittal parameters. PURPOSE The purpose of this study was to compare immediate restoration of segmental (SL) and regional lordosis (RL) after single level MIS TLIF using an expandable or static interbody cage. STUDY DESIGN/SETTING All patients underwent single level MIS TLIF using tubular retractor and bilateral pedicle screw fixation with interbody cage. Measurements of preoperative RL and SL were made and compared with post operative values. Patients were divided into 3 groups based on their preoperative SL: low lordosis ( 25°). Mann Whitney u test was used to determine statistical significance of results PATIENT SAMPLE Patients who underwent single level MIS TLIF. OUTCOME MEASURES Segmental and regional lordosis after single level MIS TLIF using an expandable or static interbody cage METHODS A retrospective review of prospectively collected data on patient undergoing single level MIS TLIF using expandable or static interbody cages was performed. All patients underwent single level MIS TLIF using tubular retractor and bilateral pedicle screw fixation with interbody cage. Measurements of preoperative RL and SL were made and compared with post operative values. Patients were divided into 3 groups based on their preoperative SL: low lordosis ( 25°). Mann Whitney u test was used to determine statistical significance of results. RESULTS A total of 114 patients were included with 57 patients in the expandable cohort and 53 in the static cohort. The expandable cohort had an average age of 64 (37–86) and 34 females. The static cohort had an average age of 58 (24–80) and 27 females. In the expandable cage cohort, patients who had low lordosis preoperatively had a statistically significant increase in postoperative SL (p CONCLUSIONS This study compares the immediate impact of MIS TLIF using expandable or static cages on segmental lordosis of the lumbar spine. Our findings suggest that while cage type does not impact postoperative lordosis, a patient's preoperative lordosis can. Specifically, those patients with low lordosis preoperatively (>15°) have the highest likelihood of achieving statistically significant improvement in segmental lordosis while those with moderate (15–25°) or high (>25°) lordosis preoperatively may experience no change or even a loss of lordosis postoperatively.

BACKGROUND CONTEXT Anterior cervical decompression and fusion (ACDF) is one of the most successful and widely performed spine surgeries. Although high rates of fusion have been reported, there is a risk for pseudarthrosis. Urinary cross-linked n-telopeptide of type I collagen (uNTx), is an important marker of bone turnover and may prove useful as a predictor of fusion in pts undergoing ACDF. PURPOSE The purpose of present study was to examine the association of preop uNTx level and successful fusion after ACDF. STUDY DESIGN/SETTING Prospective cohort study. PATIENT SAMPLE Adult patients who underwent ACDF with allograft and plating technique. OUTCOME MEASURES Fusion status was assessed using radiographic criteria published by Song et al. METHODS Patients undergoing primary ACDF with allograft and plating technique from 2015 to 2017 by a single surgeon were consecutively enrolled and preop uNTx was measured. Revision cases, improperly timed uNTx collection, pts with a Cr>1.2 were excluded. Demographics, operative, laboratory and fusion data was assessed at 6 months, 1 year and 2 years. NDI and VAS outcome scores were compared between fusion and nonfusion groups. Regression analysis was performed to assess the association of preop uNTx and successful fusion. RESULTS Of the 97 patients enrolled, 67 met inclusion criteria and were studied. 41%, 33%, 18% and 8% underwent one, two, three and four level ACDFs, respectively. Fusion rates were 37.3% at 6 months (n=67), 70.9% at 1 year (n=55) and 95.3% at 2 years (n=43). The preop uNTx was higher in the fusion group at 6mo (31 vs. 22, p CONCLUSIONS Urinary NTx was higher in patients with successful ACDF fusion compared to patients with radiographic pseudarthrosis at 6 months and 1 year. A linear relationship between uNTx levels and Fusion was observed. Surgeons should consider measuring uNTx prior to cervical fusion procedures to identify patients at risk for pseudarthrosis.

The transforaminal posterior approach (TLIF) procedure was first described in 1982. Current literature indicates its equality in outcomes for fusion constructs as other anterior-posterior procedures. As a procedure becomes more popular and is more frequently performed the types and number of complications that occur increase. We report on a two case series that underwent TLIF. Both patients had satisfactory postoperative imaging, but presented later with coronal plane vertebral body fractures in the caudal vertebral body of the TLIF construct. We believe the complication may be related to: (a) unrecognized fracture of the endplate during cage impaction; (b) overloading the endplates by maximizing the lordosis achieved by using the reverse jackknife position on a Jackson table; (c) underlying mineral bone disease in patients. As the TLIF procedure increases in popularity, caution should be exercised to avoid the same potential complications. To describe a potential complication with the TLIF procedure. Case report. 2. Revision surgery. Case series. Caudal vertebral body fracture is a potential complication after TLIF. TLIF procedures can result in an unstable vertebral body fracture potentially necessitating revision decompression & stabilization. We recommend extra caution in patients with mineral bone disease, as technical errors can be magnified.

IntroductionRestoration of sagittal balance is paramount in any type of spinal reconstructive surgery. Recent work has demonstrated that the failure to maintain lumbar lordosis following fusion not...

We construct an internal language for cartesian closed bicategories. Precisely, we introduce a type theory modelling the structure of a cartesian closed bicategory and show that its syntactic model satisfies an appropriate universal property, thereby lifting the Curry-Howard-Lambek correspondence to the bicategorical setting. Our approach is principled and practical. Weak substitution structure is constructed using a bicategorification of the notion of abstract clone from universal algebra, and the rules for products and exponentials are synthesised from semantic considerations. The result is a type theory that employs a novel combination of 2-dimensional type theory and explicit substitution, and directly generalises the Simply-Typed Lambda Calculus. This work is the first step in a programme aimed at proving coherence for cartesian closed bicategories.