@online{ptf-collision-response,
    author = "Randy Gaul",
    title  = "How to Create a Custom 2D Physics Engine: The Basics and Impulse Resolution",
    howpublished = "\url{http://goo.gl/G0gdWU}"
}


@online{ptf-Resource-Acquisition,
    author = "tomdalling",
    title  = "Resource Acquisition is Initialisation (RAII) Explained",
    howpublished = "\url{http://goo.gl/Oh5FpP}"
}

@online{ptf-Creating-City,
    author = "Daniel Mansfield",
    title  = "Creating a City Building Game with SFML",
    howpublished = "\url{https://goo.gl/TUj4lj}"
}

@online{ptf-ImpulseEngine,
    author = "RandyGaul",
    title  = "ImpulseEngine"
    howpublished = "\url{https://goo.gl/UvOGk4}",
}

@online{ptf-Game-Physics-Stability,
    author = "Allen Chou",
    title  = "Game Physics: Stability – Slops",
    howpublished = "\url{http://goo.gl/jOaEGA}"
}

@online{ptf-Game-Loop,
    author = "entropyinteractive-Eric",
    title  = "The Game Loop",
    howpublished = "\url{http://goo.gl/cin0jt}"
}