Add "Switch" method,also add "define_f"(for Felsch specific requirements)
Add "Switch" method,also add "define_f"(for Felsch specific requirements)

sampadsaha5/sympy,yashsharan/sympy,chaffra/sympy,yashsharan/sympy,sampadsaha5/sympy,rahuldan/sympy,jaimahajan1997/sympy,madan96/sympy,jaimahajan1997/sympy,souravsingh/sympy,chaffra/sympy,aktech/sympy,postvakje/sympy,skidzo/sympy,rahuldan/sympy,chaffra/sympy,postvakje/sympy,rahuldan/sympy,drufat/sympy,souravsingh/sympy,postvakje/sympy,drufat/sympy,madan96/sympy,aktech/sympy,kaushik94/sympy,yashsharan/sympy,aktech/sympy,jaimahajan1997/sympy,sampadsaha5/sympy,kaushik94/sympy,kaushik94/sympy,souravsingh/sympy,skidzo/sympy,drufat/sympy,madan96/sympy,skidzo/sympy