Mission

Bridging Classical Euclidean Elements and Modern Circle, Projective & Triangle Geometry

geometor/casey establishes the authoritative Digital Scriptorium edition and exact symbolic engine for John Casey’s A Sequel to the First Six Books of the Elements of Euclid (1888 / 1892) within the GEOMETOR canon.

1. Historical Bridge Across the Canon: Before Nathan Altshiller-Court codified College Geometry (1925 / 1952, geometor/altshiller-court) and Clark Kimberling indexed 50,000+ triangle centers (geometor/etc), John Casey’s Sequel (first published in 1881 and brought to maturity in the 1886–1892 editions with the Supplementary Chapter on the Recent Elementary Geometry of the Triangle) was the premier English-language treatise organizing post-Euclidean synthetic geometry book-by-book onto Euclid’s Elements (geometor/euclid, geometor/elements) while absorbing the projective discoveries of Poncelet, Chasles, Monge, Desargues, Pascal, and Brianchon (geometor/pappus).

2. 100% Exact Symbolic Euclidean Circle Algebra: Every geometric invariant in geometor.casey—the power of a point $d^2 - r^2$, circle orthogonality $d^2 = r_1^2 + r_2^2$, radical axes, Poncelet limiting points, circular inversion, pole–polar bilinear reciprocity, Casey’s generalized Ptolemy bitangent determinant, Feuerbach’s tangency $|NI| = R_9 - r$, and Lemoine–Brocard–Steiner–Tarry coordinates—is computed in 100% exact SymPy rational and algebraic arithmetic with zero float or sp.Float approximations inside Model.

3. Strict Content / Code Separation: Following GEOMETOR Digital Scriptorium standards, the 6-unit 3-Track Book Codex (docsrc/sequel_to_euclid/) preserves faithful historical enunciations, demonstrations, calibrated interactive .euclid-graphic SVGs, structured summaries, and cross-repository commentary with zero embedded Python scripts, while executable @proposition constructions and symbolic proofs live cleanly in src/geometor/casey/, demos/, and docsrc/demos/.