Evolution of the convective core size in mass coordinate as a function of central hydrogen content during the main sequence phase for the two considered convective boundary definition criteria: Ledoux (solid blue lines) and Schwarzschild (solid red lines). Blue dotted lines depict semiconvective zones when the Ledoux criterion is applied. (By definition there are no semiconvective zones when the Schwarzschild criterion is applied.) The panels represent different masses: 1.2 M_⊙ (top), 1.5 M_⊙ (middle), and 2.0 M_⊙ (bottom).