Beam: I_rect=b·h³/12; σ_max=6·M/(b·h²); w_cant=P·L³/(3EI); P_cr=π²·EI/L²

Sympy-exact symbolic witness of the Euler-Bernoulli beam canonical identities for cross-section geometry, maximum bending stress, deflection, and Euler buckling. Setup: b_rect, h_rect, M, E, I, L, P — all positive symbols. Rectangular…