public MathTask Next()
{
_step++;
MathTask t = null;
do
{
var op = GetNextOperationType();
switch (op)
{
case Operation.Add: t = new Add(op, level); break;
case Operation.Substract: t = new Substract(op, level); break;
case Operation.Multiply: t = new Mult(op, level); break;
case Operation.Divide: t = new Divide(op, level); break;
case Operation.Prime: t = new Prime(op, level); break;
case Operation.Perimeter: t = new Perimeter(op, level); break;
}
t.GenerateArgs(_step, _random);
} while (hs.Contains(t.GetHashCode()));
_tasks.Add(t);
hs.Add(t.GetHashCode());
return(t);
}