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# 1 OpenMath functionality in GAP

After loading the package:

    gap> LoadPackage( "openmath" );
    true

the following operations are available.

- `OMPrint(` obj`) F`

  OMPrint writes the XML OpenMath encoding of GAP object obj to the standard output.

      gap> g := Group((1,2,3));;
      gap> OMPrint(g);
      <OMOBJ>
      	<OMA>
      		<OMS cd="group1" name="Group"/>
      		<OMA>
      			<OMS cd="permut1" name="Permutation"/>
      			<OMI> 2</OMI>
      			<OMI> 3</OMI>
      			<OMI> 1</OMI>
      		</OMA>
      	</OMA>
      </OMOBJ>

- `OMGetObject(` stream`) F`

  stream is an input stream (see InputTextFile, InputTextUser, InputTextString, InputOutputLocalProcess ) with an OpenMath object on it. OMGetObject takes precisely one object off stream and returns it as a GAP object. Both XML and binary OpenMath encoding are supported, autodetection is used. This function requires that the external program `gpipe`, included in this package, has been compiled.

  This may be used to retrieve objects from a file, for example:

      gap> test3:=Filename(DirectoriesPackageLibrary("openmath","tst"),"test3.omt");;
      gap> stream := InputTextFile( test3 );;
      gap> OMGetObject(stream);
      912873912381273891
      gap> OMGetObject(stream);
      E(4)
      gap> CloseStream(stream);

  or it can be used to retrieve them from standard input - one may paste an OpenMath object directly into standard input after issuing GAP with the following commands:

      gap> stream := InputTextUser();;
      gap> g := OMGetObject(stream);CloseStream(stream);

- `OMPutObject(` stream`,` obj`) F`

  OMPutObject writes (appends) the XML OpenMath encoding of the GAP object obj to output stream stream (see OutputTextFile, OutputTextUser, OutputTextString, InputOutputLocalProcess ).

      gap> g := [[1,2],[1,0]];;
      gap> t := "";
      ""
      gap> s := OutputTextString(t, true);;
      gap> OMPutObject(s, g);
      gap> CloseStream(s);
      gap> Print(t);
      <OMOBJ>
      	<OMA>
      		<OMS cd="linalg2" name="matrix"/>
      		<OMA>
      			<OMS cd="linalg2" name="matrixrow"/>
      			<OMI> 1</OMI>
      			<OMI> 2</OMI>
      		</OMA>
      		<OMA>
      			<OMS cd="linalg2" name="matrixrow"/>
      			<OMI> 1</OMI>
      			<OMI> 0</OMI>
      		</OMA>
      	</OMA>
      </OMOBJ>

- `OMTest(` obj`) F`

  Converts obj to OpenMath and back. Returns true iff obj is unchanged (as a GAP object) by this operation. The OpenMath standard does not stipulate that converting to and from OpenMath should be the identity function so this is a useful diagnostic tool.

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