WOLFRAM LANGUAGE MESSAGE
- This message is generated by an attempt to assign a value to a protected symbol.
- A symbol s is protected if Attributes[s] includes Protected.
- An assignment tag is the symbol to which an assignment attaches an evaluation rule.
- A function::write message can be generated indirectly by any function that makes assignments.
- Off[message] switches off the message; On[message] switches it on. For example: Off[General::write].
The use of k+1 as an iterator generates an error when Do tries to assign a value to that iterator: