let S be non empty non void ManySortedSign ; :: thesis: for U0 being non-empty MSAlgebra over S
for U1, U2 being MSSubAlgebra of U0 holds U1 /\ (U1 "\/" U2) = MSAlgebra(# the Sorts of U1, the Charact of U1 #)

let U0 be non-empty MSAlgebra over S; :: thesis: for U1, U2 being MSSubAlgebra of U0 holds U1 /\ (U1 "\/" U2) = MSAlgebra(# the Sorts of U1, the Charact of U1 #)
let U1, U2 be MSSubAlgebra of U0; :: thesis: U1 /\ (U1 "\/" U2) = MSAlgebra(# the Sorts of U1, the Charact of U1 #)
reconsider u1 = the Sorts of U1, u2 = the Sorts of U2 as MSSubset of U0 by Def9;
A1: the Sorts of (U1 /\ (U1 "\/" U2)) = the Sorts of U1 (/\) the Sorts of (U1 "\/" U2) by Def16;
( u1 c= the Sorts of U0 & u2 c= the Sorts of U0 ) by PBOOLE:def 18;
then u1 (\/) u2 c= the Sorts of U0 by PBOOLE:16;
then reconsider A = u1 (\/) u2 as MSSubset of U0 by PBOOLE:def 18;
U1 "\/" U2 = GenMSAlg A by Def18;
then A is MSSubset of (U1 "\/" U2) by Def17;
then A2: A c= the Sorts of (U1 "\/" U2) by PBOOLE:def 18;
the Sorts of U1 c= A by PBOOLE:14;
then the Sorts of U1 c= the Sorts of (U1 "\/" U2) by ;
then A3: the Sorts of U1 c= the Sorts of (U1 /\ (U1 "\/" U2)) by ;
reconsider u112 = the Sorts of (U1 /\ (U1 "\/" U2)) as MSSubset of U0 by Def9;
A4: the Charact of (U1 /\ (U1 "\/" U2)) = Opers (U0,u112) by Def16;
the Sorts of (U1 /\ (U1 "\/" U2)) c= the Sorts of U1 by ;
then the Sorts of (U1 /\ (U1 "\/" U2)) = the Sorts of U1 by ;
hence U1 /\ (U1 "\/" U2) = MSAlgebra(# the Sorts of U1, the Charact of U1 #) by ; :: thesis: verum