Giuseppe Peano (1858–1932) was an Italian mathematician and logician who wanted maths spelled out so precisely that not a single hidden assumption could sneak in. He gave us the rules that define the counting numbers themselves — and a taste for symbols so strong he tried to invent a whole new language.
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Peano loved to break intuitions. He constructed a single continuous curve — now called a space-filling curve — that manages to pass through every point of a solid square without leaving any gaps. A line, in other words, thick enough to be a surface. It stunned mathematicians and forced everyone to rethink what "dimension" even means. In later life he also poured energy into "Latino sine flexione," a stripped-down universal Latin he hoped scientists everywhere would use — a logician's dream of a perfectly regular language.