Also I make use of the definition symbol "≡" to define features. Simplest situation is file(x) ≡ y. I'm applying it to point out a connection to search out sums instead of stating it as the sum that we are deriving however it may be used to point out equivalence. https://zanerybwh.blogs-service.com/67268108/the-greatest-guide-to-por-qué-es-bueno-leer-el-tarot