[r85804306610]

maxima has logic package, written in 2009 by alexey beshenov. it lives in share/logic which is also where the texi docs are. it's included with the op version,

  load(logic);
  logic_simp (a or (b or false or (a or b)));
  characteristic_vector (a xor b);
  zhegalkin_form ((a implies b) or c);
  e : ((a or b) xor c) and d$
  logic_equiv (e, zhegalkin_form (e));
  logic_diff (a or b or c, a);
  demorgan (boolean_form (a nor b nor c));

etc. there's more stuff in docs