open System;let f x = ([1..x]|>Seq.iter(fun _->Console.Write 'x'))in[1..10]|>Seq.iter(fun x->f x;([18..-1..2*x-1]|>Seq.iter(fun _->Console.Write ' '));f x;Console.WriteLine());;
Standard input is empty
x x xx xx xxx xxx xxxx xxxx xxxxx xxxxx xxxxxx xxxxxx xxxxxxx xxxxxxx xxxxxxxx xxxxxxxx xxxxxxxxx xxxxxxxxx xxxxxxxxxxxxxxxxxxxx