L1 = {a^n b^m | n<=m} can be rewritten as
{a^n b^m | n<m} U {a^n b^m | n=m}
this part {a^n b^m | n<m} contains all strings in which b is greater
this part {a^n b^m | n=m} contains all strings in which ais equal to b
L2 = {a^n b^m | n>m} = {aab,aaabb,aaab.........}
L1 U L2 =(a*b*)