• To: mathgroup at smc.vnet.net
• Subject: [mg75120] Re: question about Protect
• From: Daniel Huber <dh at metrohm.ch>
• Date: Wed, 18 Apr 2007 04:54:10 -0400 (EDT)
• References: <f013jm\$8f5\$1@smc.vnet.net>

```Hi Dimitris,
it seems like Integrate protects Limit. What is strange is, that the
protection works only once. Looks like a bug to me:
Unprotect[Limit];
Attributes[Limit]
Integrate[1/Sqrt[Abs[x]],{x,-1,2}]
Attributes[Limit]
Unprotect[Limit];
Attributes[Limit]
Integrate[1/Sqrt[Abs[x]],{x,-1,2}]
Attributes[Limit]
Daniel

dimitris wrote:
> Hello.
>
> The following code add a rule for the Limit command
>
> In[1]:=
> Off[General::spell1]
> Unprotect[Limit];
> Limit[a___] := Null /; (Print[InputForm[limit[a]]]; False)
>
> For example
>
> In[7]:=
> Integrate[1/Sqrt[Abs[x]], {x, -1, 2}]
>
>>From In[7]:=
> InputForm[limit[1 + (1 + x)/2 + (3*(1 + x)^2)/8, x -> -1, Direction ->
> -1, Assumptions -> True]]
>>From In[7]:=
> InputForm[limit[(-I)/Sqrt[x], x -> 0, Direction -> 1, Assumptions ->
> True]]
>>From In[7]:=
> InputForm[limit[I/Sqrt[x], x -> 0, Assumptions -> True]]
>>From In[7]:=
> InputForm[limit[2*Sqrt[x], x -> 1, Direction -> 1, Assumptions ->
> True]]
>>From In[7]:=
> InputForm[limit[2*Sqrt[x], x -> 0, Direction -> -1, Assumptions ->
> True]]
>>From In[7]:=
> InputForm[limit[1/Sqrt[x], x -> 0, Direction -> -1, Assumptions ->
> True]]
>>From In[7]:=
> InputForm[limit[1/Sqrt[x], x -> 0, Assumptions -> True]]
>>From In[7]:=
> InputForm[limit[1/Sqrt[2] - (-2 + x)/(4*Sqrt[2]) + (3*(-2 + x)^2)/
> (32*Sqrt[2]), x -> 2, Direction -> 1, Assumptions -> True]]
>>From In[7]:=
> InputForm[limit[2*Sqrt[x], x -> 2, Direction -> 1, Assumptions ->
> True]]
>>From In[7]:=
> InputForm[limit[2*Sqrt[x], x -> 0, Direction -> -1, Assumptions ->
> True]]
>
> Out[7]=
> 2*(1 + Sqrt[2])
>
> Note that I have NOT protect the Limit command. Nevertheless,
>
> In[8]:=
> Clear[Limit]
> Clear::wrsym: Symbol Limit is Protected.
>
>
> Why do we get this message? How Limit was protected WITHOUT telling
> so?
>
> In[12]:=
> Information["Limit", LongForm -> True]
>
> "Limit[expr, x->x0] finds the limiting value of expr when x approaches
> x0."*Button[More..., ButtonData :> "Limit",
>    Active -> True, ButtonStyle -> "RefGuideLink"]
> Attributes[Limit] = {Listable, Protected}
> Limit[a___] := Null /; (Print[InputForm[limit[a]]]; False)
> Options[Limit] = {Analytic -> False, Assumptions :> \$Assumptions,
> Direction -> Automatic}
>
> Of course
>
> In[19]:=
> Unprotect[Limit];
> Clear[Limit];
> Protect[Limit];
>
> In[22]:=
> Information["Limit", LongForm -> True]
>
> "Limit[expr, x->x0] finds the limiting value of expr when x approaches
> x0."*Button[More..., ButtonData :> "Limit",
>    Active -> True, ButtonStyle -> "RefGuideLink"]
> Attributes[Limit] = {Listable, Protected}
> Options[Limit] = {Analytic -> False, Assumptions :> \$Assumptions,
> Direction -> Automatic}
>
> but the question still remains!
>
>

```

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