``` jnml@3900x:~$ panic: code=.tnotebook3 select -1 -> r= err=Managed window index "-1" out of bounds goroutine 1 [running, locked to thread]: modernc.org/tk9%2e0.fail(...) /home/jnml/pkg/mod/modernc.org/tk9.0@v0.55.3/tk.go:418 modernc.org/tk9%2e0.evalErr({0xc0003266f0, 0x15}) /home/jnml/pkg/mod/modernc.org/tk9.0@v0.55.3/tk.go:405 +0x337 modernc.org/tk9%2e0.(*TNotebookWidget).Select(0xc0001d2000, {0x601dc0?, 0xc000307bd0?}) /home/jnml/pkg/mod/modernc.org/tk9.0@v0.55.3/tk.go:5452 +0x10d main.(*app).selectToolbox(...) /home/jnml/pkg/mod/modernc.org/equ@v1.1.0/gui.go:146 main.(*app).selectPriorToolbox(...) /home/jnml/pkg/mod/modernc.org/equ@v1.1.0/gui.go:140 modernc.org/tk9%2e0.newEventHandler.func1(0x60d660?) /home/jnml/pkg/mod/modernc.org/tk9.0@v0.55.3/tk.go:618 +0x13 modernc.org/tk9%2e0.eventDispatcher(0x1?, 0x1?, 0x2, 0x1e98c60) /home/jnml/pkg/mod/modernc.org/tk9.0@v0.55.3/tk_purego.go:313 +0x323 reflect.Value.call({0x60eb40?, 0x752738?, 0xc0000cb498?}, {0x658cb9, 0x4}, {0xc000329f20, 0x4, 0xc000329f20?}) /usr/local/go/src/reflect/value.go:581 +0xca6 reflect.Value.Call({0x60eb40?, 0x752738?, 0x7fff4cdb8588?}, {0xc000329f20?, 0xc0003f69c0?, 0x0?}) /usr/local/go/src/reflect/value.go:365 +0xb9 github.com/ebitengine/purego.callbackWrap(0x7fff4cdb84d8) /home/jnml/pkg/mod/github.com/ebitengine/purego@v0.8.0/syscall_sysv.go:178 +0x3ab github.com/ebitengine/purego.syscall_syscall15X(0x7fcfc8c4a0e0, 0x1e8cbf0, 0x7fcf9f4013b0, 0xf, 0x40000, 0x0, 0x0, 0x0, 0x0, 0x0, ...) /home/jnml/pkg/mod/github.com/ebitengine/purego@v0.8.0/syscall_sysv.go:24 +0x1e5 github.com/ebitengine/purego.SyscallN(0x7fcfc8c4a0e0, {0xc000112160?, 0x40?, 0x48573d?}) /home/jnml/pkg/mod/github.com/ebitengine/purego@v0.8.0/syscall.go:52 +0x15b modernc.org/tk9%2e0.eval({0xc0001a4170?, 0xf}) /home/jnml/pkg/mod/modernc.org/tk9.0@v0.55.3/tk_purego.go:242 +0x112 modernc.org/tk9%2e0.evalErr({0xc0001a4170, 0xf}) /home/jnml/pkg/mod/modernc.org/tk9.0@v0.55.3/tk.go:403 +0x2f modernc.org/tk9%2e0.(*Window).Wait(0xd6c370?) /home/jnml/pkg/mod/modernc.org/tk9.0@v0.55.3/tk.go:1191 +0x212 main.(*app).gmain(0xc0000fa480, 0x5e99ad?) /home/jnml/pkg/mod/modernc.org/equ@v1.1.0/gui.go:106 +0xfbf main.(*app).main(0xc0000fa480?, 0x7fff4cdba348?) /home/jnml/pkg/mod/modernc.org/equ@v1.1.0/main.go:171 +0x245 main.main() /home/jnml/pkg/mod/modernc.org/equ@v1.1.0/main.go:111 +0x54a ^C [1]+ Ukončena 2 equ -dark -g '\sum_{k=1}^n k^2={1 \over 2} n(n+1).' jnml@3900x:~$ ```