RE: why Pi is not recognized as a positive number?

• To: mathgroup at smc.vnet.net
• Subject: [mg45364] RE: [mg45360] why Pi is not recognized as a positive number?
• From: "David Park" <djmp at earthlink.net>
• Date: Sat, 3 Jan 2004 01:35:07 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

```Peter,

x_Positive is the pattern for an expression that has the Head Positive - not

f[x_?Positive] := x + 1

f[Pi]
1 + Pi

David Park

From: Pedro L [mailto:pedrito6 at softhome.net]
To: mathgroup at smc.vnet.net

I wanted to define a function for the positive numbers. But I discovered
something "strange" with Mathematica.

Could you help me with this?

Peter L  (Spain)

{

Cell[CellGroupData[{
Cell[BoxData["\$Version"], "Input",
CellLabel->"In[1]:="],

Cell[BoxData["\<\"5.0 for Microsoft Windows (June 11, 2003)\"\>"], \
"Output",
CellLabel->"Out[1]="]
}, Open  ]],

Cell[BoxData[
RowBox[{
RowBox[{"f", "[", "x_Positive", "]"}], ":=",
RowBox[{"x", "+", "1", "  "}]}]], "Input",
CellLabel->"In[2]:="],

Cell[CellGroupData[{

Cell[BoxData[
RowBox[{"Positive", "[", "Pi", "]"}]], "Input",
CellLabel->"In[3]:="],

Cell[BoxData["True"], "Output",
CellLabel->"Out[3]="]
}, Open  ]],

Cell[CellGroupData[{

Cell[BoxData[
RowBox[{"f", "[", "Pi", "]"}]], "Input",
CellLabel->"In[4]:="],

Cell[BoxData[
RowBox[{"f", "[", "\[Pi]", "]"}]], "Output",
CellLabel->"Out[4]="]
}, Open  ]],

Cell[BoxData[
RowBox[{"Remove", "[", "f", "]"}]], "Input",
CellLabel->"In[5]:="],

Cell[BoxData[
RowBox[{
RowBox[{"f", "[",
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RowBox[{"x", ">", "0"}]}], "]"}], ":=",
RowBox[{"x", "+", "1"}]}]], "Input",
CellLabel->"In[6]:="],

Cell[CellGroupData[{

Cell[BoxData[
RowBox[{"f", "[", "Pi", "]"}]], "Input",
CellLabel->"In[7]:="],

Cell[BoxData[
RowBox[{"1", "+", "\[Pi]"}]], "Output",

CellLabel->"Out[7]="]
}, Open  ]],

Cell[BoxData[
RowBox[{"Remove", "[", "f", "]"}]], "Input",
CellLabel->"In[8]:="]
}

```

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