reserve x,y for set;
reserve C,C9,D,D9,E for non empty set;
reserve c for Element of C;
reserve c9 for Element of C9;
reserve d,d1,d2,d3,d4,e for Element of D;
reserve d9 for Element of D9;
reserve i,j for natural Number;
reserve F for Function of [:D,D9:],E;
reserve p,q for FinSequence of D,
  p9,q9 for FinSequence of D9;
reserve f,f9 for Function of C,D,
  h for Function of D,E;
reserve T,T1,T2,T3 for Tuple of i,D;
reserve T9 for Tuple of i, D9;
reserve S for Tuple of j, D;
reserve S9 for Tuple of j, D9;
reserve F,G for BinOp of D;
reserve u for UnOp of D;
reserve H for BinOp of E;

theorem
  F is associative & F is having_a_unity & F is having_an_inverseOp
  implies (F*(id D,the_inverseOp_wrt F)).(d,d) = the_unity_wrt F
proof
  assume
A1: F is associative & F is having_a_unity & F is having_an_inverseOp;
  set u = the_inverseOp_wrt F;
  thus F*(id D,u).(d,d) = F.(d,u.d) by Th81
    .= the_unity_wrt F by A1,Th59;
end;
