Propositions

A proposition is a symbolic event over a frame.

frame = Frame.dsmt(["A", "B", "C"])
A, B, C = frame.symbols()

Operators

Use | for union and & for intersection:

A | B
A & B
(A | B) & C

Small habit, fewer surprises: use parentheses in compound expressions, especially when mixing | and &.

Model-dependent meaning

The frame decides whether intersections are possible.

dst = Frame.dst(["A", "B"])
dsmt = Frame.dsmt(["A", "B"])

dst_a, dst_b = dst.symbols()
dsmt_a, dsmt_b = dsmt.symbols()

str(dst_a & dst_b)   # "empty"
str(dsmt_a & dsmt_b) # "A&B"

String expressions

String parsing is useful for config files, notebooks, and user input:

frame.proposition("A | B")
frame.proposition("A & (B | C)")
frame.proposition("A ∩ (B ∪ C)")

Supported syntax:

  • atom names from the frame,

  • &, ∩, ∧ for intersection,

  • |, ∪, ∨ for union,

  • parentheses,

  • empty or ∅.

The parser uses the same precedence as the object operators: intersection binds before union.

Coercion

Most methods accept propositions, strings, or iterables of atom names:

frame.mass({"A": 0.4, "B": 0.2, "A | B": 0.4})
frame.mass({A: 0.4, B: 0.2, A | B: 0.4})
frame.proposition(["A", "B"]) # A|B

Best default: use object expressions in library code and string expressions when reading from outside the program.

Display

str(A | B)       # "A|B"
str(A & B)       # "A&B" in free DSmT, "empty" in DST
format(A | B)    # same string formatting behavior as str(...)

Hybrid model constraints are reflected in the displayed proposition.