Dave Peterson wrote...
....
But even simpler:
=isnumber(match("*" & a1 & "*",b1:b100,0))
will return true/false
....

But even shorter still,

=COUNTIF(B1:B100,"*"&A1&"*")0

will return True/False with a single function call. Now it may not
recalc as quickly, but there are times when nested function calls must
be kept to a minimum.