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Visual science, equals (26/40) Before the equals symbol was invented, mathematicians would use useful and expressive words as an indication of what was going on. When adding, they used "yields" or "gives". Other earlier symbols for equality included "æ" parallel lines pointing up were also used. These days an increasing number of mathematicians have become skeptical that the equal sign, traditionally used to show exact relations between sets of things, holds up to modern mathematical models. A wave of mathematicians are turning to the idea of category theory, based in understanding the relationships between different objects. This would super seed set theory at dealing with equivalence, as it is more universally applicable to alternate branches of maths.