if a ~= b then -- Do something end if not boolean_expression then -- Do something end if not (a == b) then -- Do something end-- if-then if a < 0 then a = 0 end -- if-then-else if a < b then return a else return b end -- if-then-elseif-then-else if a < 0 then x = 0 elseif a > 1 then x = 1 else x = a end