R:(A*
A*Prop).
(EquivRel x,y:A*. x R y) 
(x,y,z:A*. (x R y) ((z @ x) R (z @ y)))
(g:((x,y:A*//(x R y))
). Sym u,v:x,y:A*//(x R y). u Rg v)
lquo_rel_symm
a,b:T. E(a;b) E(b;a)
Thm* R:(A*A*Prop).
(EquivRel x,y:A*. x R y)
(x,y,z:A*. (x R y) ((z @ x) R (z @ y)))
(g:((x,y:A*//(x R y))). Sym u,v:x,y:A*//(x R y). u Rg v)
lquo_rel_symm
Thm* L:LangOver(A). Sym x,y:A*. x L-induced Equiv y lang_rel_symm
In prior sections: rel 1 relation autom