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    <link:label id="lab_pro_LicenseAndImplementationExpenseMember_534EFDFE85E03DD65895D86C2358E814_documentation_en-US" xlink:label="lab_pro_LicenseAndImplementationExpenseMember_534EFDFE85E03DD65895D86C2358E814" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">License and implementation [Member]</link:label>
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    <link:label id="lab_pro_CostOfRevenueDomain_BA54B2238B3CADD41382D86C23586969_label_en-US" xlink:label="lab_pro_CostOfRevenueDomain_BA54B2238B3CADD41382D86C23586969" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Cost of revenue [Domain]</link:label>
    <link:label id="lab_pro_CostOfRevenueDomain_BA54B2238B3CADD41382D86C23586969_documentation_en-US" xlink:label="lab_pro_CostOfRevenueDomain_BA54B2238B3CADD41382D86C23586969" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Cost of revenue [Domain]</link:label>
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    <link:label id="lab_pro_SellingMarketingGeneralAndAdministrativeExpenseMember_44BB9A2F58D06D60C84CD86C235896BA_terseLabel_en-US" xlink:label="lab_pro_SellingMarketingGeneralAndAdministrativeExpenseMember_44BB9A2F58D06D60C84CD86C235896BA" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Selling, marketing, general and administrative</link:label>
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    <link:label id="lab_pro_SellingMarketingGeneralAndAdministrativeExpenseMember_44BB9A2F58D06D60C84CD86C235896BA_documentation_en-US" xlink:label="lab_pro_SellingMarketingGeneralAndAdministrativeExpenseMember_44BB9A2F58D06D60C84CD86C235896BA" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Selling, marketing, general and administrative expense [Member]</link:label>
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    <link:label id="lab_pro_OperatingExpensesDomain_73D7F01ABBC992FB9B8DD86C23586604_label_en-US" xlink:label="lab_pro_OperatingExpensesDomain_73D7F01ABBC992FB9B8DD86C23586604" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Operating expenses [Domain]</link:label>
    <link:label id="lab_pro_OperatingExpensesDomain_73D7F01ABBC992FB9B8DD86C23586604_documentation_en-US" xlink:label="lab_pro_OperatingExpensesDomain_73D7F01ABBC992FB9B8DD86C23586604" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Operating expenses [Domain]</link:label>
    <link:loc xlink:href="pro-20140331.xsd#pro_OperatingExpensesDomain" xlink:label="loc_pro_OperatingExpensesDomain_73D7F01ABBC992FB9B8DD86C23586604" xlink:type="locator" />
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    <link:label id="lab_us-gaap_LeasesAbstract_C2E98A5DBFA1F1C052D5E289A477EB70_label_en-US" xlink:label="lab_us-gaap_LeasesAbstract_C2E98A5DBFA1F1C052D5E289A477EB70" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Leases [Abstract]</link:label>
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    <link:label id="lab_us-gaap_PartiesToContractualArrangementAxis_4B3DE0214FBE8247A5A3E289A478FF1F_terseLabel_en-US" xlink:label="lab_us-gaap_PartiesToContractualArrangementAxis_4B3DE0214FBE8247A5A3E289A478FF1F" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Parties to Contractual Arrangement [Axis]</link:label>
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    <link:label id="lab_us-gaap_SalesRevenueNetAbstract_2A7C4DB18C47CD30590AE187DCF59E51_label_en-US" xlink:label="lab_us-gaap_SalesRevenueNetAbstract_2A7C4DB18C47CD30590AE187DCF59E51" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Revenue, Net [Abstract]</link:label>
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