Thorough analysis of input physics in CESAM and CLES codes

This contribution is not about the quality of the agreement between stellar models computed by CESAM and CLES codes, but more interesting, on what ESTA-Task~1 run has taught us about these codes and about the input physics they use. We also quantify the effects of different implementations of the same physics on the seismic properties of the stellar models, that in fact is the main aim of ESTA experiments.