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===Intuitionistic Propositional Calculus===
 
===Intuitionistic Propositional Calculus===
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<pre>
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{| align="center" cellpadding="8" width="90%" <!--QUOTE-->
| An 'intuitionistic propositional calculus' is more than a
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| positive one;  it requires also falsehood and disjunction,
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| that is, a formula 'F' (= false) and an operation 'v' (= or)
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| on formulas, together with the following additional arrows:
   
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|          []_A
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<p>An ''intuitionistic propositional calculus'' is more than a positive one;  it requires also falsehood and disjunction, that is, a formula <math>\bot</math> (&nbsp;=&nbsp;false) and an operation <math>\lor</math> (&nbsp;=&nbsp;or) on formulas, together with the following additional arrows:</p>
| R5.    F ------> A,
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|-
 
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|          k1_A,B
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<p><math>\begin{array}{ll}
| R6a.   A --------> A v B,
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\text{R5.}  & \bot ~\xrightarrow{~\Box_A~}~ A;
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\\[8pt]
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\text{R6a.} & A ~\xrightarrow{~\kappa_{A, B}~}~ A \lor B,
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\\[8pt]
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\text{R6b.} & B ~\xrightarrow{~\kappa'_{A, B}~}~ A \lor B,
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\\[8pt]
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\text{R6c.} & (C \Leftarrow A) \land (C \Leftarrow B) ~\xrightarrow{~\zeta^C_{A, B}~}~ C \Leftarrow (A \lor B).
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\end{array}</math></p>
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|-
 
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|          k2_A,B
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<p>(Lambek & Scott, 49&ndash;50).
| R6b.  B --------> A v B,
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|}
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|                            !z!^C_A,B
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| R6c.  (C <= A) & (C <= B) -----------> C <= (A v B).
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</pre>
      
===Classical Propositional Calculus===
 
===Classical Propositional Calculus===
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