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+# OcctSurfaces
+
+The OcctSurfacer intersects B-Rep parts and shows a full list of relations in
+two possible notations, named and syllogical.
+
+## The idea behind OcctSurfacer
+
+1. Named notation have such possible results to show for each surface pair:
+
+- **Equals**: means two surfaces are completely equal, including their
+  orientation; A\B (A substracted to B) is empty as B\A too.
+
+- **Negates**: means surfaces don't leave any substraction results (A\B = B\A =
+  empty) but also A and B have different orientation (e.g. a cylinder part side
+  surface and a cylinder hole side surface with the same diameters)
+
+- **Included/Includes**: means A\B (or B\A) is empty while B\A (or A\B) is not,
+  so B includes A (or A includes B)
+
+- **Crosses**: intersection of A and B is not a surface
+
+- **Intersects**: intersection of A and B is a surface, but A\B and B\A both is
+  not empty
+
+- **Irrelates** intersection of A and B is empty
+
+2. Logical notation (AIEO) is a simpler option to show the same thing in classic
+   syllogical terms:
+
+- A Includes B = "all A are (has) B" = A "A" "B"
+- A Included in B = "all B are (has) A" = A "B" "A"
+- A Equals B = "all A are B, and vice versa" = (A "A" "B") and (A "B" "A")
+- A Negated B = "No A are B" = E "A" "B" = E "B" "A"
+- A Crosses B = "No A are B" = E "A" "B" = E "B" "A"
+- A Intersects B = "there's an I subsurface which is a part of A (so A has I),
+  and part of B too (so A has I). however, there're subsufaces A1 and B1 which
+  are parts of A and B too": (A "A" "I") and (A "B" "I") and (A "B" "B0") and (A
+  "A" "A0")
+
+## Usage
+
+To list relations with their names, send a B-Rep filenames list to stdin with
+`-named` arg:
+
+```sh
+OcctSurfacer -named < brep_filename_list.txt
+```
+
+By default, `Irrelates` relations are hidden. To show it too, pass `-irrelates`
+after `-named`:
+
+```sh
+OcctSurfacer -named -irrelates < brep_filename_list.txt
+```
+
+--------------------------------------------------------------------------------
+
+The main objective of OcctSurfacer is *extracting facts*, so to use logical
+notation you can pass it without additional arguments:
+
+```sh
+OcctSurfacer < brep_filename_list.txt
+```
+
+## Building and installation
+
+### nix/NixOS flakes
+
+```sh
+nix run "git+https://forgejo.gregorbednov.ru/gregorbednov/OcctSurfacer" -- -named -irrelates
+```
+
+### classic build
+
+You need a [OpenCASCADE Techology
+OCCT](https://occt3d.com/open-cascade-technology/), CMake, OpenMP (optional),
+and C++ compiler.
+
+```sh
+cmake -B build -S .
+make
+./OCCTSurfacer # to run it
+make install # or to install it
+```