If that's true it's a trade-off which may or may not be worth it. It's not inherently bad or unacceptable.
Many other skills require a period of re-learning after a five year gap. Where do you believe K sits on the scale of re-learning effort involved, riding-a-bike seconds to minutes, or months to years of effort?
I've only learned a little APL so far, and that really didn't take much effort so I'd be surprised if it would take me more than a month of dedicated learning to get fluent in the language. If that's what it takes to learn from scratch (the language, not the concepts common to maths and many programming languages), I would expect re-learning to be possible in less than a week. That does not strike me as too big an obstacle in many cases.
Many other skills require a period of re-learning after a five year gap. Where do you believe K sits on the scale of re-learning effort involved, riding-a-bike seconds to minutes, or months to years of effort?
I've only learned a little APL so far, and that really didn't take much effort so I'd be surprised if it would take me more than a month of dedicated learning to get fluent in the language. If that's what it takes to learn from scratch (the language, not the concepts common to maths and many programming languages), I would expect re-learning to be possible in less than a week. That does not strike me as too big an obstacle in many cases.