h='able to fly'
i="(not )?(#{h}|\\w+)"
o=->s{n=Regexp.new(i+" (is also|are) "+i).match s
[[n[2],!n[1]],[n[5],!n[4]]]}
c=e=!z=[]
w=->r{z.member?(r)||(z<<(a,b=r)
c|=a[0]==b[0]&&a[1]!=b[1]
w[[[b[0],!b[1]],[a[0],!a[1]]]]
z.map{|q|q[1]==r[0]&&w[[q[0],r[1]]]})}
y=->x{z.member?([[p='Pigs',!e],[h,x]])}
f=->x{x.split(?.).map{|s|w[o[s]]}
c|y[!e]?'Yes':y[e]?'No':'Maybe'}
 
 
def assert_equal(x, y)
  fail "Not equal: <#{x.inspect}> != <#{y.inspect}>" if x != y
  puts "OK."
end
test=->(text, exp){
  c=!z=[] # (re) initialization needed for multiple test runs
  assert_equal(f[text], exp)
}
 
test['Pigs are green. Everything that is green is also intelligent. Everything that is able to fly is also not intelligent.', 'No']
test['Pigs are old. Everything that is not able to fly is also not old.', 'Yes']
test['Everything that is sweet is also not old. Everything that is intelligent is also blue.', 'Maybe']
test['Pigs are not able to fly. Everything that is red is also sweet. Everything that is sweet is also not red.', 'Yes']
test['Pigs are very smart. Pigs are able to fly.', 'Yes'] # <-- any answer accepted here
 

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