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module map;

auto map(FT, ATR)(FT f, ATR x)
if(isInputRange!ATR && is(typeof(f(x.front))) && !is(typeof(f(x.front)) == void))
{
    static struct R
    {
        auto front()
        {
            return f(x.front);
        }
        void popFront()
        {
            x.popFront;
        }
        bool empty()
        {
            return x.empty();
        }

      private:
        FT  _f;
        ART _x;
    }
    return R(f, x);
}