span style="font-weight: normal;">This is a 
 secondary option for controlling the degree to which the fitter flattens 
 a design netlist. A logic gate can collapse forward into a subsequent 
 gate only if the number of inputs in the resulting logic function does 
 not exceed the input limit. If the design fails to fit the target device 
 because flattening uses up too many of the function block inputs, decrease 
 the input limit to prevent flattening of certain high fan-in functions. 
 </span><!--kadov_tag