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+#### How to make an API change that involves a form factor
+
+This note shall help when you
+* add a form factor
+* remove a form factor
+* change a form factor's argument list
+
+After adding or removing a form factor, the following files need to be updated:
+* Core/Basics/BornAgainNamespace.h
+* Core/Parametrization/INodeVisitor.h (in two places)
+* Core/includeIncludes/HardParticles.h
+* Wrap/swig/libBornAgainCore.i (in two places: #include and %include)
+
+If the form factor is supported by the GUI, then also:
+* GUI/coregui/Models/GUIDomainSampleVisitor.h
+* GUI/coregui/Models/GUIDomainSampleVisitor.cpp