kill(all)$

van=facebook.com/LearningCalculus$

assume(x>0,y>0)$

A(x,y,a):=x+y=a$
B(x,y  ):=x^x=y^y$

A(x,y,a);

solve([A(x,y,4),B(x,y)],[x,y]);

solve(x^x=(x-a)^(x-a),x);

Log(a,u):=log(u)/log(a);

Log(x,x^x=(x-a)^(x-a));

%, logexpand=super;

logcontract(%);

fullratsimp(%);