#4p1s0: # Already optimal matching forward
   (?:   a  (?: ble | n(?:ce|t) | te | l )
     |   e  (?: ment | n(?:ce|t) | r )
     |   i  (?: ble | sm | ti | ve | ze | c )
     |   ment
     |   ous?
   )
#4p0s1r: # No performance gains matching in reverse
   (?:   (?: elb | (?:ec|t)n | et | l )  a
     |   (?: tnem | (?:ec|t)n | r )  e
     |   (?: elb | ms | it | ev | ez | c )  i
     |   tnem
     |   s?uo
   )
#4p1s0r: # Likewise this is not an optimal match, although:
   (?:   ci
     |   e  (?: cn[ae] | lb[ai] | ta | vi | zi )
     |   iti
     |   la
     |   msi
     |   re
     |   suo   
     |   tn  (?: eme? | [ae] )
     |   uo
   )
#4p0s1: # It's better than this:
   (?:ic|(?:[ae]nc|[ai]bl|at|iv|iz)e|iti|al|ism|er|ous|(?:e?me|[ae])nt|ou)

##</code><code>##

#3p0s1: # Less optimal
(?:   (?: icat | ativ | aliz )  e
  |   iciti
  |   (?: ica | fu )  l
  |   ness
)
#3p1s0r: # More optimal - performance gains in reverse
(?:   e  (?: taci | vita | zila )
  |   itici
  |   l  (?: aci | uf )
  |   ssen
)

##</code><code>##

   (?:abcd|efg|won|I|[now]|know|my|regexes)
   (?:abcdcba|efgfe|wonow|[now]|I|knowonk|mym|regexesexeger)
   (?x-ism: dcba|gfe |     now |I| [own] |wonk|y m|sexeger)

##</code><code>##

#!/usr/bin/perl
use Regex::PreSuf;
my @step4list   =qw(
   al able ance ant ate
   ence ent ement er
   ible ic ism iti ive ize
   ment
   ou ous
);
grep $_=reverse, @step4list;
print "4p1s0r:", presuf ({suffixes=>0}, @step4list), "\n";
print "4p1s1r:", presuf ({suffixes=>1}, @step4list), "\n";
print "4p0s1r:", presuf ({prefixes=>0}, @step4list), "\n";