Let R, S, T be relations in T and let x be a letter. If R is functional in x in T, show that the following relations are theorems in T :
(not (∃x)(R and S))⇔(∃x)(R and (not S)),
(∃x)(R and (S and T))⇔(∃x)(R and S) and (∃x)(R and T)),
(∃x)(R and (S or T))⇔((∃x)(R and S) or (∃x)(R and T)).
Nothing.
Nothing.