"... the laws of physics and of logic ... the number system ... the principle of algebraic substitution. These are ghosts. We just believe in them so thoroughly they seem real."

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It had grown darker as they talked, and the wind was sawing and the sawdust was whirling outside paler windows. The underlying churchyard was already settling into deep dim shade, and the shade was creeping up to the housetops among which they sat. "As if," said Eugene, "as if the churchyard ghosts were rising."

— Charles Dickens