EFFICIENCY!!!

#! /usr/local/bin/a+ -q

$mode ascii

unique{x}:((x iota x)= iota #x)/x
nl{x}:,"\n",@1 x

 'found these functions in /u/apter';
btom{x}:>( max/># each x) take each x
vtoe{y;x}:if (`null= ? x) x else 1 drop each ( bag x in y) bag x := (( iota (1 take x) in y)/1 take y),x
vtom{y;x}:btom{vtoe{y;x}}
noLines{x}:vtom{"\n";(-"\n"=(-1) take x) drop x}

a := 0 rho ''
(n := (-1)+#_argv) do {
  a[,] := nl sys.readmat >_argv[n+1];
}

if (0 ~= rho a) {
  unique noLines a
}

sys.exit 0

That's funny, I was looking into A+ just yesterday for some reason.