Is a hot dog a sandwich? Let’s examine one of the hardest problems in metaphysics to find out. Because THUNK.
The Stanford Encyclopedia of Philosophy is invaluable for getting a broad understanding of this topic quickly. Some key pages I found helpful:
Metaphysics Overview - https://plato.stanford.edu/entries/metaphysics/ Platonism in Metaphysics - https://plato.stanford.edu/entries/platonism/ Abstract Objects - https://plato.stanford.edu/entries/abstract-objects/ Nominalism in Metaphysics - https://plato.stanford.edu/entries/nominalism-metaphysics/ Tropes - https://plato.stanford.edu/entries/tropes/
The n-tuple representation of tropes was from Tropes: Properties, Objects, & Mental Causation by Douglas Ehring - http://goo.gl/zzYJpp
Is This a Sandwich? Teaching the Platonic Dialogues through sandwiches (M Ritchey, 2014) - https://medium.com/snack-lords/is-this-a-sandwich-50b1317eb3f5
A Bro And A Philosopher Debate The True Meaning Of A Sandwich (Scherer, 2015) - https://firstwefeast.com/eat/2015/04/philosophy-of-meat-bread
Also, I sorta gloss over defining metaphysics, which is a challenging work of philosophy in its own right - https://www.youtube.com/watch?v=RFKSo2084Kg
“There Exists An X, X is a Sandwich,” by Joel K Jensen (thanks, grammaticalcrimes!) - http://goo.gl/zX7wcc