py-logic 0.1.1

Library to use and simulate propositional logic

logic

Logic is a predicate logic simulator. It can be used to create automated proof.

Installation

Install using pip with the git url

pip install py-logic

Example Usage

from logic import Proposition, IMPLY, prove


# Creating propositional variables
a = Proposition("a")
b = Proposition("b")

assumptions = [
  IMPLY(a, b), # if a then b
  ~b,          # not b
]

conclusion = ~a # not a

# generating proof
proof, truth = prove(assumptions, conclusion)

print(proof)

Output

Using Modus Tollens the above conclusion can be proved:

               ¬ (a)                Modus Tollens {((a) → (b)), ¬ (b)}     

---

This is question from Discrete Mathematics and Its Applications 7th Edition by Kenneth H. Rosen.

If Superman were able and willing to prevent evil, he would do so. If Superman were unable to prevent evil, he would be impotent; if he were unwilling to prevent evil, he would be malevolent. Superman does not prevent evil. If Superman exists, he is neither impotent nor malevolent. Therefore, Superman does not exist.

Code to solve the above question

from logic import Proposition, IMPLY, prove


# Creating propositional variables
a = Proposition("a", "Superman is able to prevent evil")
b = Proposition("b", "Superman is willing to prevent evil")
c = Proposition("c", "Superman is impotent")
d = Proposition("d", "Superman is malevolent")
e = Proposition("e", "Superman prevents evil")
f = Proposition("f", "Superman exists")

# encoding assumptions
assumptions = [
    IMPLY(a & b, e),
    IMPLY(~e, c),
    IMPLY(~b, d),
    ~e,
    IMPLY(f, ~c & ~d),
]

# encoding conclusion
conclusion = ~f

# printing assumptions
print("Assumptions:")
for i in assumptions:
    print(i)

# printing conclusion
print(f"Conclusion: {conclusion}")

# generating proof
proof, truth = prove(assumptions, conclusion)
assert truth == True # checking if it could be proved

# printing proof
print(proof)

TODO

• Implement support for ForAll and ThereExists
• Implement proof verifier, to verify proof given by user