定理的语法类似于定义的语法，除了签名中的共域（即定理陈述）是强制性的。

command ::= ...
    | `declModifiers` is the collection of modifiers on a declaration:
* a doc comment `/-- ... -/`
* a list of attributes `@[attr1, attr2]`
* a visibility specifier, `private` or `public`
* `protected`
* `noncomputable`
* `unsafe`
* `partial` or `nonrec`

All modifiers are optional, and have to come in the listed order.

`nestedDeclModifiers` is the same as `declModifiers`, but attributes are printed
on the same line as the declaration. It is used for declarations nested inside other syntax,
such as inductive constructors, structure projections, and `let rec` / `where` definitions. declModifiers
      theorem `declId` matches `foo` or `foo.{u,v}`: an identifier possibly followed by a list of universe names declId `declSig` matches the signature of a declaration with required type: a list of binders and then `: type` declSig := termTermination hints are `termination_by` and `decreasing_by`, in that order.

command ::= ...
    | `declModifiers` is the collection of modifiers on a declaration:
* a doc comment `/-- ... -/`
* a list of attributes `@[attr1, attr2]`
* a visibility specifier, `private` or `public`
* `protected`
* `noncomputable`
* `unsafe`
* `partial` or `nonrec`

All modifiers are optional, and have to come in the listed order.

`nestedDeclModifiers` is the same as `declModifiers`, but attributes are printed
on the same line as the declaration. It is used for declarations nested inside other syntax,
such as inductive constructors, structure projections, and `let rec` / `where` definitions. declModifiers
      theorem `declId` matches `foo` or `foo.{u,v}`: an identifier possibly followed by a list of universe names declId `declSig` matches the signature of a declaration with required type: a list of binders and then `: type` declSig
        (| term => term)*Termination hints are `termination_by` and `decreasing_by`, in that order.

command ::= ...
    | `declModifiers` is the collection of modifiers on a declaration:
* a doc comment `/-- ... -/`
* a list of attributes `@[attr1, attr2]`
* a visibility specifier, `private` or `public`
* `protected`
* `noncomputable`
* `unsafe`
* `partial` or `nonrec`

All modifiers are optional, and have to come in the listed order.

`nestedDeclModifiers` is the same as `declModifiers`, but attributes are printed
on the same line as the declaration. It is used for declarations nested inside other syntax,
such as inductive constructors, structure projections, and `let rec` / `where` definitions. declModifiers
      theorem `declId` matches `foo` or `foo.{u,v}`: an identifier possibly followed by a list of universe names declId `declSig` matches the signature of a declaration with required type: a list of binders and then `: type` declSig where
        structInstField*

在 modules 中，默认情况下不公开定理证明。