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We establish a general method for simultaneously perturbing a convergent sequence of functions in such a way that the sequence of strong minima of the perturbed functions tend to the strong minimum of their limit.

Properties of local and global slope of a function and its approximate critical points sets are studied in relation to determination of the function.

We study Orlicz functions that do not satisfy the $\Delta_2$-condition at zero. We prove that for every Orlicz function $M$ such that $\limsup_{t\to0}M(t)/t^p >0$ for some $p\ge1$, there exists a positive sequence $T=(t_k)_{k=1}^\infty$ tending to zero and such that $$ \sup_{k\in\mathbb{N}}\frac{M(ct_k)}{M(t_k)} <\infty,\text{ for all }c>1, $$ that is, $M$ satisfies the $\Delta_2$ condition with respect to $T$. Consequently, we show that for each Orlicz function with lower Boyd index $\alpha_M < \infty$ there exists an Orlicz function $N$ such that: (a) there exists a positive sequence $T=(t_k)_{k=1}^\infty$ tending to zero such that $N$ satisfies the $\Delta_2$ condition with respect to $T$, and (b) the space $h_N$ is isomorphic to a subspace of $h_M$ generated by one vector. We apply this result to find the maximal possible order of G\^ateaux differentiability of a continuous bump function on the Orlicz space $h_M(\Gamma)$ for $\Gamma$ uncountable.

We develop a new perturbation method in Orlicz sequence spaces $\ell_M$ with Orlicz function $M$ satisfying $\Delta_2$ condition at zero. This result allows one to support from below any bounded below lower semicontinuous function with bounded support, with a perturbation of the defining function $\sigma_M$. We give few examples how the method can be used for determining the type of the smoothness of certain Orlicz spaces.

We present a proof of Hadamard Inverse Function Theorem by the methods of Variational Analysis, adapting an idea of I. Ekeland and E. Sere.

We consider the classical Inverse Function Theorem of Nash and Moser from the angle of some recent development by Ekeland and the authors. Geometrisation of tame estimates coupled with certain ideas coming from Variational Analysis when applied to a directionally differentiable function, produce very general surjectivity result and, if injectivity can be ensured, Inverse Function Theorem with the expected Lipschitz-like continuity of the inverse. We also present a brief application to differential equations., Comment: This is revised version. Implicit Mapping Theorem and an application to ODE were added

We present a new method for proving Correa-Jofr\'e-Thibault theorem that monotonicity of subdifferential implies convexity of the function. This new method is based on barrier functions. Barrier functions help overcome some of the main technical difficulties when working with lower semicontinuous functions.

We provide a new proof along the lines of the recent book of A. Ioffe of a 1990's result of H. Frankowska showing that metric regularity of a multi-valued map can be characterized by regularity of its contingent variation - a notion extending contingent derivative.

We present simple and direct proof to an important case of Nash-Moser-Ekeland theorem., Comment: In this third version we have made numerous improvements inspired by the referee, like correcting the definition of directional derivative to the standard one and proving more general statement. The method of proof, however, is the same

We prove surjectivity result in Fr\'echet spaces of Nash-Moser type. That is, with uniform estimates over all semimorms. Our method works for functions which are only continuous and G\^ateaux differentiable like in the recent result of Ekeland. We present the results in multi-valued setting exploring the relevant notions of map regularity., Comment: The main correction in this version is clarifying that our definition of G\^ateaux differentiability is stronger than the standard one

We provide a new proof for maximal monotonicity of the subdifferential of a convex function.