theorem Lemma4: :: LATWAL_1:4

for L being non empty LattStr st ( for v1, v0 being Element of L holds v0 "/\" v1 = v1 "/\" v0 ) & ( for v0 being Element of L holds v0 "\/" v0 = v0 ) & ( for v1, v0 being Element of L holds v0 "\/" v1 = v1 "\/" v0 ) & ( for v2, v1, v0 being Element of L holds ((v0 "/\" v1) "\/" (v2 "/\" v1)) "\/" v1 = v1 ) holds
for v1, v2 being Element of L holds v1 "\/" (v1 "/\" v2) = v1